1. Field of the Invention
This invention relates to a novel class of tractable linear aromatic polyesters of improved fire safety performance as well as to molding powders and shaped articles produced therefrom and is more particularly concerned with amorphous and crystalline polyesters comprising recurring units derived from 1,2-bis(hydroxyphenyl)ethanes and molding powders and shaped articles derived therefrom.
2. Description of the Prior Art
Many polyesters have been suggested for use as molding resins and engineering thermoplastics since the earliest practical development of such polymers by Whinfield and Dickson. Although several of such polyesters and copolyesters have found commercial success as film and fiber products, few have been successful as molding resins and engineering thermoplastics. Two of the more successful, polyethylene terephthalate and polytetramethylene terephthalate prepared from aliphatic diols and terephthalic acid, suffer from certain deficiencies as engineering thermoplastics. They are both quite flammable and have rather low glass transition temperatures which limit their usefulness to relatively low temperatures.
U.S. Pat. No. 3,160,602 discloses a process of forming polyesters by reaction of diphenol and aromatic carboxyl dihalide in solvent at temperatures of 270.degree. C. or higher. The preferred polyesters are derived from hydroquinone and isophthalic acid and resorcinol and terephthalic acid and cocondensates where part of the hydroquinone or resorcinol is replaced by another dihydric phenol and part of the isophthalic or terephthalic acid has been replaced with another dicarboxylic acid. The patent suggests that the process might be used for the reaction of aromatic carboxyl dihalides and an extremely broad class of dihydric phenols of the general formula: ##STR3## However, the instability of alkylene bridged diphenols at such high reaction temperatures in the presence of hydrogen halide would prevent the formation of polyesters of adequate molecular weight and acceptable color and indeed degradation of such polyesters under severe reaction conditions is recognized in Belgian Pat. No. 766,806 by the common assignee.
Drewitt and Lincoln, U.S. Pat. No. 2,595,343, teach a more satisfactory method of preparing polyesters from diphenols, by reacting the diacetates of the diphenols with dicarboxylic acids.
Polyesters prepared from diphenols and aromatic dicarboxylic acids are in general useful at higher temperatures because of their higher softening temperatures. However, unless they comprise flame retardants which yield toxic off-gases containing nitrogen, sulfur, phosphorus or halogen, they also are fairly flammable, particularly when they are in the form of thin sheets or filaments. Such polyesters include the polyesters of bisphenol A (2,2'-bis(4-hydroxyphenyl)propane) and of 1,1-bis(4-hydroxyphenyl)ethane. Moreover, many polyesters such as the polyesters of hydroquinone, 4,4'-dihydroxydiphenyl, bis(4-hydroxyphenyl)methane and the like have extremely high softening points often above 400.degree. C. and are therefore thermally unstable in the melt, and impractical for conventional processing since they are intractable at conventional processing temperatures.
French Pat. No. 2,006,477 discloses new 1,4-dicarboxy-1,4-dialkylcyclohexanes and polymers prepared therefrom. Among the polymers, is a flammable polyester prepared from 1,2-bis (4-hydroxyphenyl)ethane and the alicyclic acid 1,4-dimethylcyclohexane 1,4-dicarboxylic acid. Kolesnikov et al disclose polycarbonates and mixed polycarbonates of 1,2-bis(4-hydroxyphenyl)ethane (Polymer Science A, USSR 9,764-773 (1967), but do not associate flame retarding properties with them.
A need, therefore, exists in the art for an engineering thermoplastic polyester which is flame retardant without addition of toxic flame retardant elements such as halogen and phosphorus and which has a relatively high glass transition temperature to allow it to be useful at temperatures above 100.degree. C.
In a review of methylene bridged diphenol polyesters in Industrial and Engineering Chemistry (Vol. 51-1959 p. 147) Andre Conix, reported twenty-nine diphenol polyesters. Only two (bisphenol A terephthalate and bisphenol A/benzophenone-4, 4-dicarboxylic acid) were found to be crystalline while a third, amorphous (bisphenol A isophthalate) could be obtained from solution in a semi-crystalline state by a solution casting technique. The author recognized that the influence of chemical structure on physical behavior such as crystallinity is rather complicated and not easily predictable.
Conix, in U.S. Pat. No. 3,448,077 teaches that polyesters obtained from aromatic dicarboxylic acids and diphenols are amorphous but may be crystallized by heat treatment.
A need therefore exists for a polyester engineering thermoplastic which is relatively high melting to provide high temperature strength but not so high as to be intractable or degrade on melting and which is amorphous or is rapidly crystallized so that it can be molded on conventional molding equipment at rapid molding cycles.
A further need exists for a polyester engineering thermoplastic which contains a high degree of crystallinity for solvent and chemical resistance and for dimensional stability of molded or shaped articles.
A further need exists for a rapidly crystallizing, crystalline polyester engineering t ermoplastic which has improved fire safety performance without addition of toxic flame retardant elements such as nitrogen, sulfur, phosphorus or halogen.